Device for checking the pitch diameter of a screw thread

ABSTRACT

A DEVICE FOR CHECKING THE SIMPLE PITCH EFFECTIVE DIAMETER OF INTERNAL AND EXTERNAL THREADS MEASURES A PARAMETER OF A FLUID MEDIUM IN THE CLEARANCE BETWEEN A THREAD BEING MEASURED AND A MASTER THREAD. INCLUDED IN THE DEVICE IS A HOLDER WITH A MASTER THREAD WHICH MATCHES AND MATES WITH THE THREAD BEING MEASURED. THE HOLDER HAS PASSAGES FOR THE FLUID MEDIUM AND NOZZLES ARE ARRANGED DIAMETRICALLY OPPOSITE EACH OTHER ON THE FLANKS OF A NUMBER OF ADJACENT MASTER THREAD RIDGES SO THAT THEY END SHORT OF RIDGE CRESTS. THE NOZZLES ARE USED TO FEED THE FLUID MEDIUM UNDER PRESSURE INTO THE CLEARANCE BETWEEN THE MASTER THREAD AND THE THREAD BEING MEASURED. SHUTTERS CAPABLE OF MOVING RADIALLY WITH RESPECT TO THE NOZZLES ARE CONTAINED IN THE DEVICE AND ARE DESIGNED TO CLOSE THE CLEARANCE BETWEEN THE MASTER THREAD AND CRESTS OF THE THREAD BEING MEASURED. FLUID IS DISCHARGED FROM THE CLEARANCE BETWEEN THE THREAD BEING MEASURED AND THE MASTER THREAD AND A PARAMETER OF THE FLUID WHICH DEPENDS UPON THE AMOUNT OF CLEARANCE BETWEEN THE FLANKS OF THE THREAD BEING MEASURED AND THOSE OF THE MASTER THREAD IS MEASURED.

Sept. 1911 m. SQROZOVSKY EI'AL 3,608,356

DEVICE FOR CHECKING THE PITCH DIAMETER OF A SCREW THREAD 4 Sheets-Sheet 1 Filad March 24, 1970 J J"! J m u. M. m 7 y $\u V H Sept. 28, 1911 I 5, ozovs ETAL 3,608,356

DEVICE FOR CHECKING THE PITCH DIAMETER OF A SCREW THREAD Filed March 24, 1910 4 Sheets-Sheet a M.s. ROZOVSKY ETA!- ,356

DEVICE FOR CHECKING THE PITCH DIAMETER OF A SCREW THREAD Sept. 23,1971

4 Sheets-Sheet 3 Filed Hag-ch 24. 1970 Q mt Sept. 28, 1971 RQZOVSKY ETAL 3,608,356

-' DEVICE FOR CHECKING THE PITCH DIAMETER OF A SCREW THREAD Filed March-24, 1970 4 Sheets-Sheet I.

United States Patent 3,608,356 DEVICE FOR CHECKING THE PITCH DIAMETER OF A SCREW THREAD Max Solomonovich Rozovsky, Novobasmannaya ulits'a 14, kv. 32; Valeria Grigorievna Lapteva, Fryazevskaya ulitsa 32, korpus 3, kv. 9; and Oleg Prokofievich Fedosov, Novorgozhskaya ulitsa 5, kv. 93, all of Moscow, U.S.S.R.

Filed Mar. 24, 1970, Ser. No. 22,323 Int. Cl. G01b 13/12, 13/00 US. Cl. 73-37.9 1 Claim ABSTRACT OF THE DISCLOSURE A device for checking the simple pitch efiective diameter of internal and external threads measures a parameter of a fluid medium in the clearance between a thread being measured and a master thread. Included in the device is a holder with a master thread which matches and mates with the thread being measured. The holder has passages for the fluid medium and nozzles are arranged diametrically opposite each other on the flanks of a number of adjacent master thread ridges so that they end short of ridge crests. The nozzles are used to feed the fluid medium under pressure into the clearance bet-ween the master thread and the thread being measured. Shutters capable of moving radially with respect to the nozzles are contained in the device and are designed to close the clearance between the master thread and crests of the thread being measured. Fluid is discharged from the clearance between the thread being measured and the master thread and a parameter of the fluid which depends upon the amount of clearance between the flanks of the thread being measured and those of the master thread is measured.

The present invention relates to non-contact pneumatic devices for checking the pitch diameter of a screw thread under the conditions of both conventional and automated manufacture in various branches of engineering.

There exists a pneumatic non-contact device for checking the pitch diameter of a screw thread (see Izmerenie tugikh rezb by M. E. Katsnelson, Moscow, 1957).

The known device comprises a holder with a thread of a profile matching that of the thread being checked. Diametrically arranged nozzles in the form of small circular holes are cut through both sides of a thread ridge. The nozzles are in communication with a passage for feeding the working medium. The known device in fact gauges the complex pitch diameter. The latter is evaluated by measuring some certain condition of the working medium in the clearance between the axial cross-sections of the thread being checked and the master thread at a point on each flank of a thread.

The results of measurements taken by the known pneumatic non-contact device may be influenced by any possible inaccuracy in the pitch and flank angle. The pitch error has a direct bearing on the measurement results as the measurements are taken on both sides of the axis at one thread ridge only.

The magnitude of the flank angle error depends on the location of the nozzles in the thread sides.

The above-mentioned disadvantages make impossible the use of the known device for measuring the simple pitch diameter which is the basic dimension of a screw thread, particularly when it is desirable to obtain an interference fit.

There also exist different contact-type device for measuring the simple pitch diameter of a screw thread but they are either insufiiciently accurate or timeand labour-consuming in operation.

An object of the present invention is to provide a de- 3,668,356 Patented Sept. 28, 1971 vice ensuring accurate measurement of the simple pitch diameter of a screw thread.

Another object of the present invention is to provide a device which makes the measurement of the simple pitch diameter of a screw thread not a labour-consuming operation.

A further object of the present invention is to provide devices in which the contact between the flanks of the thread under check and those of the master thread is eliminated.

A still further object of the invention is to provide devices capable of accomplishing the measurement procedure within a short time.

The above-mentioned objects are accomplished byproviding a device for non-contact measurement of the simple pitch diameter of a screw thread, comprising a holder with a thread matching the thread being checked and two nozzles arranged diametrically in thread flanks to let a fluid medium, compressed and fed through a passage in said holder, escape into a clearance between said holder and the thread being checked.

The device disclosed herein differs from the known devices in that the nozzles are given the shape of slots and they are arranged diametrically opposite each other along the thread axis in a plane pass-ing through said thread axis, each said slot extending through a number of adjacent thread ridges; the crests of the ridges through which the slot passes are left uncut; and shutters are provided capable of moving radially with respect to the nozzles so as to close the clearance between the thread of said holder and crests of the thread being measured.

The device disclosed herein permits the simple pitch diameter measurements to be carried out with high accuracy and may be made for gauging both internal and external threads.

The measurement of the simple pitch diameter by means of said devices is neither labournor time-consuming. The adverse eflect of the human factor on the accuracy of measurements is fully eliminated. The flank angle and pitch errors have no bearing on the results, since the gauging is accomplished by determining the areas of clearances between the flanks of the thread being measured and those of the master thread.

The invention will be best understood from the following description of a preferred embodiment when read in conjunction with the accompanying drawings, in which:

FIG. 1 is a device for measuring the simple pitch diameter of an internal thread;

FIG. 2 is a cross-section taken on line IIII of FIG. 1;

FIG. 3 is a diagram of the process of measuring the simple pitch diameter of an internal thread;

FIG. 4 is a cross-section on line IV-IV of FIG. 3;

FIG. 5 is a device for measuring the simple pitch diameter of an external thread;

FIG. 6 is a cross-section taken on line VIVI of FIG. 5;

FIG. 7 is a diagram of the process of measuring the simple pitch diameter of an external thread;

FIG. 8 is a cross-section on line VIIIVIII of FIG. 7;

FIG. 9 is a schematic view of a pneumatic gauging system with a device for measuring the simple pitch diameter of an internal thread;

FIG. 10 is a schematic view of a pneumatic gauging system with a device for measuring the pitch diameter of an external thread;

FIG. 11 is a longitudinal sectional view of a threaded connection with a guaranteed clearance.

Described below are particular embodiments of a device for measuring the simple pitch diameter of internal and external threads, in which the fluid medium is compressed air.

Referring to FIG. 1, the device for measuring the simple pitch diameter of an internal thread comprises a holder 1 with a master thread 2 cut on it and an axially drilled passage 3 for feeding air into two diametrically arranged nozzles 4 cut in inserts 5 moving over which are shutters 6 spring-loaded in the radial direction.

The pitch diameter of the master thread 2 is somewhat smaller than the minimum limit pitch diameter of the thread being checked. This is done in order to ensure the guaranteed clearance between the master thread 2 and the thread of a work 7 (FIG. 3).

Running parallel to the axis of the holder 1 (FIG. 1) and traversing the thread 2 over its entire length are grooves 8 which provide for a free outlet of the air from the measurement zone.

The holder 1 has also annular grooves 9 (FIG. 1) to accommodate the shutters 6.

An opening 10 in the holder 1 made normally to the holder axis serves to accommodate the diametrically arranged threaded inserts 5. The thread of the inserts 5 is cut simultaneously with the thread 2 and then the former is made countersunk with respect to the latter by removing some metal from the end faces 11 of the inserts 5 within the specified allowance.

Cut through the threaded inserts 5 are the two measuring nozzles 4 made along the axis of the thread and diametrically opposite each other.

Each of the nozzles 4 is a rectangular slot of a length equal to several pitches which ends short of a crest 12 of the thread 2. The crests 12 left uncut eliminate the areas of clearances corresponding to the major diameter of the thread being measured from the measurement results.

Rectangular ports 13 provided in the inserts 5 serve to admit air into the nozzles 4.

Each pair of shutters 6 is intended to eliminate the areas of clearances corresponding to the minor diameter of the thread being measured from the measurement results.

The shutters 6 are semicircles with notches which orient them with respect to the inserts 5. Each pair of shutters is loaded by a flat spring 14 so that the shutters tend to move radially in opposite directions.

The measurement of the simple pitch diameter of an internal thread is accomplished in the following way.

The device is screwed into a bore which is to be measured, the shutters 6 (FIGS. 3 and 4) being in contact with the crests of the thread 7 being checked by the action of the springs 14 (FIGS. 1 and 2). Compressed air from a pneumatic gauging 14 system is fed into the measuring nozzles 4 (FIGS. 3 and 4) through the passage 3 (FIG. 1) and admitted from the nozzles into a clearance formed between the flanks of the thread 7 being measured and those of the master thread on the inserts 5. The uncut crests 12 eliminate the areas of clearances corresponding to the major diameter of the thread being measured and the shutters 6 eliminate the areas of clearances corresponding to the minor diameter of said thread from the measurement results.

The measurement results of the areas of the clearances between thread flanks 15 (FIG. 3) are automatically transformed into the values of the virtual pitch diameter of the thread 7 being measured and are read off the calibrated scale of a pneumatic gauge.

In the course of measurement the device can be moved along the thread 7 being measured so as to check its diameter within the specified length.

Referring to FIG. 5, the device for measuring the simple pitch diameter of an external thread comprises a holder 16 having a round bore 17 with a master thread 18 cut in it. In the holder 16, there are holes 19 which accommodate threaded inserts 20 with nozzles 21 made in the inserts. Moving over the inserts 20 are shutters 22 loaded by spring in the radial direction.

The pitch diameter of the master thread 18 is some-' what greater than the maximum limit pitch diameter of the thread being measured. This is done in order to ensure the guaranteed clearance between the master thread 18 and the thread of a work 23 (FIG. 7).

Traversing the ridges of the thread 18 (FIG. 5) throughout its length and parallel to its axis are grooves 24 which provide a free outlet for the air from the zone of measurement. The same is the function of an annular groove 25 provided at midlength of the master thread 18.

Made in one plane with the annular groove 25 are diametrically arranged bores 19. The thread of the in serts 20 is cut simultaneously with the thread 18 and the former is made countersunk with respect to the latter by means of shims 26.

Cut through the threaded inserts 20 are the two measuring nozzles 21 arranged diametrically opposite to each other.

Each of the nozzles 21 is a rectangular slot of a length equal to several pitches, which ends short of a crest 27 of the thread 18. The crests 27 left uncut eliminate the areas of clearances corresponding to the minor diameter of the thread 23 being checked from the measurement results. Rectangular ports 28 provided in the inserts 20 serve to admit air into the nozzles 21. The two shutters 22 are intended to eliminate the areas of clearances corresponding to the major diameter of the thread being checked from the measurement results.

Each of the shutters is a stepped cylinder capable of moving radially due to the action of compression spring 29. The holder 16 when assembled with the inserts 20, )shutters 22, and compression springs 29 is placed within a housing 30 fitted with a branch pipe 31 and groove 32 to admit air into the nozzles 21.

The measurement of the simple pitch diameter of an external thread is accomplished in the following way. The work 23 to be checked is screwed into the bore 17 (FIG. 5) with the master thread 18. While the work 23 is being screwed into the bore, the shutters 22 are lifted by the compressed air which is admitted through branch pipes 33- (FIG. 5) from an air line 44 (FIG. 10), by-passing the pneumatic gauging system.

As soon as the work 23 (FIG. 1) is set into the bore 17, the air supply to the shutters 22 is cut ofi and the shutters 22 bear up against the crests of the thread 23 being checked (FIG. 8).

At the same time, air is admitted into the measuring nozzles 21 and whence into the clearance formed by the flanks 34 of the thread of the work 23 being checked and of the master thread of the inserts 20.

The uncut crests 27 eliminate the areas of clearances corresponding to the minor diameter of the thread being measured and the shutters 22 eliminate the areas of clearances corresponding to the major diameter from the measurement results.

The results of measuring the areas of clearances between the thread flanks 34 are automatically transformed into the values of the virtual pitch diameter of the thread {23 being checked and read ofl the calibrated scale of the pneumatic gauge.

In the course of measurement, the work 23 can be moved relative to the master thread 18 so as to check the pitch diameter within the specified length.

The device 39 (FIG. 9) for measuring the simple pitch diameter of an internal thread is included into a gauging system comprising a moisture trap 35, a filter combined with a pressure regulator 36, a master pressure gauge 37, and a pneumatic gauge 38.

A device 45 (FIG. 10) for measuring the simple pitch diameter of an external thread is included into a gauging system comprising a moisture trap 40, a filter combined with a pressure regulator 41, a master pressure gauge 42, and a pneumatic gauge 43; a line 44 feeds air to shutters 45 by-passing the pneumatic gauging system.

The relationship existing between the simple diameter and the area of clearances between the profile of the thread being measured and that of the master thread will be better understood from FIG. 11 which shows a longitudinal sectional view of a threaded connection.

The amount of the guaranteed clearance in the threaded connection at the cross-section XI-XI normal to the axis, is represented by the diflerence between the simple pitch diameter of a nut 46 and that of a bolt 47 A=total clearance in the connection; d =simple pitch diameter of the nut; d =simple pitch diameter of the bolt.

The aggregate area of clearances F within distance 1 in the longitudinal section of the threaded connection is given by F=F1F2 where:

F =area confined between the ridges of the nut within distance I of the longitudinal section;

F area of the bolt within distance I of the longitudinal section.

Area F is the sum of parallelograms abcd, befc, emnf, and mkpn. Since the bases of the parallelograms are all equal and represent each the simple pitch diameter proper d of the bolt and the total height of the parallelograms is equal to distance I, we can write 2= 2b By analogy Then F F F l(d2 'D2 1A and Thus, the ag regate area of the clearances between the gauge and the work represents the simple pitch diameter of the work being checked.

The thread shown in FIG. 11 has the form of fundamental triangle. In fact, the thread has flats both at the crests and roots so that subject to the measurements are only the areas defined by the flanks of the thread being measured and those of the master thread, whereas the areas at the crest and root flats are eliminated.

Experimental measurements of the simple pitch diameter with the aid of the devices disclosed above have been carried out using both internal and external metric threads with a major diameter of 1 8 mm.

Example 1 is a particular embodiment of the device for measuring the simple pitch diameter of an internal metric thread with a major diameter of 18 mm.

The dimensions of the thread being measured: major diameter, (1:18 mm.; minor diameter,

+0520 mm. +0200 mm.

pitch diameter, d =16.376+- pitch, S=2.5 mm., flank angle, 30; marginal pitch diameter for sorting into Group I and Group II, d :l6.426 mm.

The dimensions of the device: pitch diameter of holder thread, d =16.356""- pitch error, less than 0.005 mm.; flank angle error, less than 9; major diameter, d=18- minor diameter, d =l5.470- amount by which the thread of each insert was made countersunk relative to the diameter of the holder thread, 0.01 mm.; width of nozzle slot, 0.35 length of nozzle slot, 1.5 pitch or 3.75 mm.; width of the flats left uncut at crests of the insert thread, 0.4- width of inserts at the zone of measurement, 1.5- width of the working edges of shutters, 0.7 mm.

The pneumatic gauging system data: air pressure,

approx. 2 bars; scale division, 1.5 microns (the scale has been calibrated by masters corresponding to the group marginal limits); maximum error of measurement of simple pitch diameter, not over 5 microns.

Example 2 is a particular embodiment of the device for measuring the simple pitch diameter of an external metric thread with a major diameter of 18 mm.

Dimensions of the thread being measured: major diameter,

0.170 mm. d- 0.450 mm.

minor diameter,

0.164 mm. 0.445 mm.

pitch diameter,

+0.196 mm. +0.095 mm.

pitch, 8:2.5 mm., flank angle, 30; marginal pitch diameter for sorting into Group I and Group II, d =16.521 mm.

The dimensions of the device: pitch diameter of holder thread, d =16.590+-" pitch error, less than 0.005 mm.; flank angle error, less than 9; major diameter, d=18+- minor diameter, d =15.144+- amount by which the thread of each insert was made countersunk relative to the diameter of the holder thread, 0.01 mm.; width of nozzle slot, 0.35+- length of nozzle slot, 1.5 pitch or 3.75 mm.; width of the flats left uncut at crests of the insert thread, 0.4"- width of inserts at the zone of measurement, 1.5-" width of the working edges of shutters, 0.7 mm.

The pneumatic gauging system data: air pressure, approx. 2 bars; scale division, 1.5 microns (the scale has been calibrated by masters corresponding to the group marginal limits); maximum error of measurement of simple pitch diameter, not over 5 microns.

What is claimed is:

1. A device for non-contact measurement of the simple pitch (effective) diameter of a screw thread by measuring a parameter of a fluid medium in the clearance between a thread being measured and a master thread, comprising a holder with a master thread matching and mating the thread being measured; said holder with a passage for the fluid medium; nozzles of rectangular cross-section which are connected to said passage, said nozzles being arranged diametrically opposite each other on the flanks of a number of adjacent master thread ridges so that they end short of the ridge crests, said nozzles being intended for feeding the fluid medium under pressure into the clearance between the master thread and the thread being measured; shutters capable of moving radially with respect to the nozzles and designed to close the clearance between the master thread and crests of the thread being measured; means for discharging the fluid medium from the clearance between the thread being measured and the master thread; means for measuring the parameter of the fluid medium which depends upon the amount of the clearance between the flanks of the thread being measured and those of the master thread.

References Cited UNITED STATES PATENTS 2,497,236 2/1950 Polk 33-Dig. 2 2,875,611 3/1959 Whitney 7337.5X 3,349,605 10/1967 Minix 7337.9 3,520,174 7/1970 Sharp et al. 7337.8 3,520,175 7/1970 Sharp et al. 7337.8

LOUIS R. PRINCE, Primary Examiner W. A. HENRY II, Assistant Examiner 

